U.S. Pat. No. 6,901,729, is incorporated herein by reference in its entirety. This patent describes a windrower. While other embodiments are possible, it is this general type of windrower that provides the best example of the type of system with which the apparatus and method of the instant invention can/should be used. U.S. Provisional Application No. 60/777,180, filed Feb. 27, 2006, is also incorporated herein by reference in its entirety.
In any modern windrower, and much other similar equipment, proportional solenoid controlled valves, activated by electrical currents, are used to control hydraulic devices such as cylinders in the actuation of various systems including the propulsion system. Associated with these valves is a range of current values that causes movement of a movable element of the valve such as a spool or barrel, without creating a path for hydraulic fluid flow between ports. The current value required to move the valve sufficiently to allow fluid communication between ports is referred to as an offset value. An offset of particular interest is the input current required to move the valve to a point in which hydraulic fluid first begins to flow.
It is important to efficient and effective operation of the system to calibrate the valve based on the offset values required to directly activate a proportional valve using electrical current. These offset values can determine the “crack” points between various ports. The “crack” points are the electrical signal levels at which two ports of interest are just beginning to open to one another from a closed position. Of particular interest are the crack points from the supply pressure port to each of the work ports and from the tank port to each of the work ports.
Therefore, it would be desirable to have a method which enables calibration of a valve based on the electrical current offset required to determine the crack points, for instance, those from the supply port to each of the working ports and from the tank port to each of the working ports.